1. Field of the Invention
The present invention relates to hearing aids. The invention, more specifically, relates to a soft custom ear mold for hearing aids. The invention further relates to a method of manufacturing a soft custom ear mold. The invention, in particular, relates to a tool for use in the method.
In the context of the present disclosure, a hearing aid should be understood as a small, battery-powered, microelectronic device designed to be worn behind or in the human ear by a hearing-impaired user. Prior to use, the hearing aid is adjusted by a hearing aid fitter according to a prescription. The prescription is based on a hearing test, resulting in a so-called audiogram, of the performance of the hearing-impaired user's unaided hearing. The prescription is developed to reach a setting where the hearing aid will alleviate a hearing loss by amplifying sound at frequencies in those parts of the audible frequency range where the user suffers a hearing deficit. A hearing aid comprises one or more microphones, a battery, a microelectronic circuit comprising a signal processor, and an acoustic output transducer. The signal processor is preferably a digital signal processor. The hearing aid is enclosed in a casing suitable for fitting behind or in a human ear.
As the name suggests, Behind-The-Ear (BTE) hearing aids are worn behind the ear. To be more precise an electronics unit comprising a housing containing the major electronics parts thereof is worn behind the ear. An ear mold for emitting sound to the hearing aid user is worn in the ear, e.g. in the concha or the ear canal. In a traditional BTE hearing aid, a sound tube is used because the output transducer, which in hearing aid terminology is normally referred to as the receiver, is located in the housing of the electronics unit. In some modern types of hearing aids a conducting member comprising electrical conductors is used, because the receiver is placed in the earpiece in the ear. Such hearing aids are commonly referred to as Receiver-In-The-Ear (RITE) hearing aids. In a specific type of RITE hearing aids the receiver is placed inside the ear canal. This is known as Receiver-In-Canal (RIC) hearing aids.
2. Prior Art
Basically two different types of ear molds are offered today. The first type may be denoted custom ear molds and are characterized in that the shape of a specific ear canal is obtained and that the ear mold is subsequently manufactured such that it corresponds to the specific ear canal. At present the shape of the ear canal is typically obtained using an ear impression but this need not be the case since e.g. various digital scanning methods can also provide the shape of a specific ear canal. The second type may be denoted instant fit ear molds and are characterized in that they have not been adapted to the shape of a specific ear canal. Instead this type of ear molds has been adapted to cover a wide range of ear canals. Generally the custom ear molds are advantageous compared to the instant fit type in that they provide a secure and precise fit in the ear canal, whereby the ear molds will not tend to fall out of the ear, and the leakage of sound around the ear mold will be small whereby the risk of acoustic feedback is reduced.
The respective custom and instant-fit ear molds may further be sub-divided into soft and hard ear molds. The hard custom ear molds may e.g. be manufactured using rapid prototyping techniques. Further details concerning such a method can be found e.g. in U.S. Pat. No. 5,487,012.
Generally the hard ear molds are advantageous in that the hard materials provide high acoustic attenuation. This is important in order to control sound leakage, and hereby acoustical feedback, from an interior sound channel in the ear mold and towards the surroundings outside the ear mold. The hard ear molds may be disadvantageous in that the hearing aid fitter will typically have to send the ear canal impressions to a remote ear mold manufacturing site, which has the consequence that the hearing aid user has to wait a few days before he can obtain his new hearing aid with hard custom ear molds.
The soft custom ear molds are typically manufactured by a hearing fitter, who obtains an impression of a specific ear canal and uses a negative of the impression to mold a soft ear mold in e.g. silicone. The soft custom ear molds are advantageous in that they may provide an improved comfort relative to hard ear molds, in that they may reduce sound leakage—even compared to hard custom ear molds, and in that local hearing aid fitters can manufacture this type of ear mold in-house. The soft ear molds may be disadvantageous in that the acoustic attenuation of the available soft ear mold materials is low compared to the available hard ear mold materials.
As already disclosed the soft ear mold is preferably manufactured in silicone. A preferred silicone is the Biopor, which is biocompatible. However, other resilient materials, such as soft acrylic may also be applied. Generally, the soft ear mold should preferably be manufactured from a material having a hardness which is below 80 measured on the Shore durometer type A scale (see the standard ASTM D2240 for description of the test). This is often written as Shore 80A. Preferably, the hardness is below Shore 60A, and more preferably the hardness is in the range from Shore 20A to Shore 45A.
In order to solve the problem of the limited acoustic attenuation of the soft ear mold materials it has been proposed in the art to insert a sound tube of a highly acoustic attenuating material into the sound conduit of the soft ear mold. It has been proposed to use e.g. Polyvinyl Chloride (PVC) and Polyurethane (PUR) as sound tube material. These materials are relatively soft and it has therefore been suggested to insert the sound tube into the soft ear mold by:                putting a hard mounting tool through the sound conduit of the ear mold such that the first end of the mounting tool is on the first side of the ear mold and the other end of the mounting tool is on the other side of the ear mold,        fixing the sound tube onto a hard mounting tool,        pulling the mounting tool, and hereby the sound tube, back through the sound conduit of the ear mold,        removing the hard mounting tool from the sound tube, and        trimming the ends of the sound tube to make them flush with the ear mold.        
In order to keep the sound tube at the correct position inside the soft ear mold it has been suggested to achieve this by:                providing a soft ear mold wherein the sound conduit is adapted to accommodate a bushing,        putting a hard mounting tool through the sound conduit of the ear mold such that the first end of the mounting tool is on the first side of the ear mold (the side adapted to face outwards when inserted in an ear canal) and the other end of the mounting tool is on the other side of the ear mold,        fixing a hard bushing to a first end of the sound tube,        engaging the first end of the mounting tool with the second end of the sound tube,        pulling the mounting tool, and hereby the sound tube and the bushing, back through the sound conduit of the ear mold until the bushing is seated correctly inside the ear mold,        removing the hard mounting tool from the sound tube, and        trimming the second end of the sound tube flush with the ear mold.        
The soft ear molds may be further be disadvantageous in that traditional ear wax guards, such as disclosed in e.g. U.S. Pat. No. 9,795,562, cannot be used. The main reason for this is that the soft ear molds are not capable of accommodating an ear wax guard or an ear wax guard bushing in the same manner as a hard ear mold. It has therefore become common practice to use the soft ear molds without an ear wax guard. A consequence of this is that the sound tube has to be cleaned regularly which is more cumbersome than simply replacing an ear wax guard.
It is therefore a feature of the present invention to overcome at least these drawbacks and provide a soft custom ear mold that permits the use of an ear wax guard.
It is another feature of the current invention to provide a method for manufacturing a soft custom ear mold.